The present invention relates generally to optical fibers and optical fiber ribbons with silane-enhanced adhesion characteristics and a method of making fibers and ribbons and, in particular, to methods of applying a silane adhesion promoter to the interface of an optical fiber coating and a glass fiber.
A single optical waveguide fiber, referred to herein as an xe2x80x9coptical fiber,xe2x80x9d can carry thousands of times more voice transmissions than a single copper conducting wire. Because of their increased capacity for voice transmissions, optical fibers have now largely replaced copper conductors in long haul telecommunications cable and are widely used for data transmission as well. Increased use of fiber optics in local loop telephone and cable TV service is expected, as local fiber networks are established to deliver ever greater volumes of information in the form of data, audio, and video signals to residential and commercial users. In addition, use of optical fibers in the home and in business for internal data, voice, and video communications has begun and is expected to increase.
Optical fiber ribbons provide a modular design which simplifies the construction, installation, and maintenance of optical fiber cable by eliminating the need to handle individual fibers. An optical fiber ribbon is constructed of a plurality of optical fibers, each of which is typically coated with one or more polymeric coatings which serve to protect and cushion the optical fiber. The plurality of coated fibers is held in a coplanar arrangement by ribbon matrix material which bonds the individual optical fibers to each other or surrounds the plurality of optical fibers in a common outer jacket or sheathing.
Use of optical fiber ribbons promises to reduce the labor and cost involved in splicing individual optical fibers, because the optical fibers in the ribbon can be spliced by connecting the much larger ribbon, provided that the positions of the optical fibers therein can be precisely fixed and maintained. In one method commonly used to splice ribbons, referred to as mass fusion splicing, the first step involves the complete removal of all protective polymer coatings and the ribbon matrix material. The process relies upon a V-block to align the individual fibers. The V-block controls angular alignment particularly well so long as the optical fiber is free of any protrusions, such as non-uniform primary coating material residue, in the region where the optical waveguide contacts the V-block. In addition, the V-block permits precise alignment of the two optical fiber ends so long as the residual primary coating material on the two ends has the same thickness. Consequently, alignment of the two optical fibers and the success of the mass fusion splice depend on the removal of the protective coatings. Indeed, if the coating materials cannot be cleanly and easily stripped, splicing operations using the V-block and other similar devices will be seriously hampered.
The adoption of fiber optics for local loop applications presents new challenges. The core of an optical waveguide fiber, or optical fiber, is usually constructed of a silica material that can be easily damaged by moisture and other environmental hazards. Protecting the optical fiber from these hazards is likely to become of increased concern, especially as the use of optical fibers in local data, audio, and video signal transmission grows. In contrast to the comparatively hermetic conditions in long distance cables, where fiber exposure points are far fewer and more sheltered, optical fibers employed in local loop applications have a larger number of splices and are more prone to attack from a variety of environmental hazards. For example, optical fiber connections are commonly made in neighborhood pedestals, which are frequently unsealed, giving insects and animals access to the optical fiber and exposing the optical fiber to moisture and water. Moreover, a substantial percentage of fiber optic cables will find installation in existing pipe chases, including pipe chases containing steam lines, where there are risks to the coatings form thermal damage, alone and in combination with high humidity, to say nothing of direct steam impingement.
Many of these environmental hazards can be remedied by coating the optical fiber. An optical fiber is typically constructed of a central core, a cladding layer, a primary (or inner primary) coating and a secondary (or outer primary) coating. The coating layers of an optical fiber serve many functions. First, the coating layers protect the optical fiber from damage and breakage during the installation of the optical fiber or ribbon and throughout the life of the fiber or ribbon. Second, the coating layers must ensure the stability of the fiber transmission characteristics. Considerations in the design of the coating layer must ensure that optical attenuation or loss of the fiber is kept to a minimum. Third, the coating layers on an optical fiber should impart mechanical properties to the optical fiber to allow ease of handling and long-term use. Bare optical fibers, comprised of the central core and cladding, are brittle and fragile. The coating on an optical fiber allows the fiber to withstand such stresses as tension, torsion, compression, bending, squeezing or vibration that it will be exposed to in the field. Lastly, the coating layers can also provide both ease of identification and joining of the fibers for an experienced field technician who needs to splice the ends of the optical fiber.
The ability of the coatings to protect the optical fiber from mechanical stresses and moisture has been correlated with the strength of the wet adhesive forces between the primary coating and the cladding layer. The adhesion of the coating to the cladding at this interface is of critical importance. If the coating pulls away or delaminates from the cladding layer, moisture can enter into the optical fiber and attack and degrade the silica glass. Delamination usually results in a weakened optical fiber because the delaminated coating can slide against the surface of the cladding causing microscopic scratches at the surface. These microscopic scratches act as crack initiation points which weaken the overall strength of the fiber. Further, delamination along the length of the fiber could cause high transmission loss or an increased attenuation.
To counter delamination and promote the adhesion of the disparate materials of the cladding and primary coating layer, manufacturers of optical fibers have added a small percentage by weight of adhesion promoting agents, such as silanes, into the primary coating composition. An optical fiber, after being formed, is subsequently coated by a primary or inner primary coating which contains silanes as part of the coating mixture. The primary coating is cured on-line via thermal or ultraviolet radiation. Curing transforms the liquid coating solution into a solid. Adhesion promoting agents in the coating solution, however, react with other constituents and have a negative impact on the cure rate of the primary coating layer. Since the coating of the optical fiber is performed on-line in a continuous process, decreasing the cure rate of the primary coating layer slows down the efficiency, rate, and cycle time of the manufacturing process.
Adhesion promoting agents may also make it difficult to remove the primary coating from the cladding layer in order to splice or rejoin the optical fiber. One of the principal drawbacks to the use of optical fibers is the difficulty in achieving an end-to-end splice with acceptable light transmission loss. For a good connection, the cores of the two fibers must be aligned very precisely or else the attenuation of the fiber increases. At present, this requires a high level of skill by the installer, as well as more time and more expensive tools relative to installations employing metallic conductors. Moreover, this problem, though important in long haul transmission fibers, is exacerbated when the fiber is used in local applications, where the number of splices per unit length of fiber installed is greatly increased.
Japanese Patent Application No. HEI 2[1990]-48434 reports a method of manufacturing an optical fiber comprising a silane coupling agent. The drawn glass fiber is passed through high-temperature vapors of a concentrated silane coupling agent to form a silane coupling agent layer on the surface of the glass fiber. The temperature at which the silane vapor is generated and applied is above the boiling temperature of the silanes but below the decomposition temperature. In addition, the silane is applied by condensation to the glass fiber as a saturated silane vapor.
The requirements of strong, adhesive bonding at the interface of the primary coating and cladding layer of the optical fiber and ease and uniform strippability have presented a difficult challenge in primary coating formulation. An additional challenge is to ensure that the adhesion promoting agent will not have a negative impact on the cure rate of the primary coating which will slow down the manufacturing process. It is preferred that the present invention is directed to meeting the dual requirements of good adhesion and ease of strippability of the primary coating layer without the negative impact on the cure rate of the primary coating by the addition of a thin, intermediary layer of an adhesion-promoting agent at the claddingxe2x80x94primary coating interface.
The present invention relates to a method of applying an adhesion-promoting intermediary layer to an optical fiber comprising providing an optical fiber and contacting the surface of the optical fiber with a mixture of an adhesion promoter and a carrier gas to form an adhesion-promoting intermediary layer. The carrier gas is preferably carbon dioxide. The adhesion promoter preferably comprises a silane including, but not limited to, azidosilane, aminoalkoxysilane, polymeric silane, polymeric organosilane, organofunctional silane, vinyl ether urethane silane, organochlorosilane, silsesquioxane, polyalkoxysiloxane, and fluorinated acrylamide silane. Preferably, the adhesion promoter comprises 1,4-bis(trimethoxysilylethyl)benzene. The mixture can be atomized and vaporized.
The present invention also relates to a method of coating an optical fiber comprising providing an optical fiber, contacting the surface of the optical fiber with a mixture of an adhesion promoter and a carrier gas to form an adhesion-promoting intermediary layer, contacting the optical fiber with a liquid acrylate, and curing the liquid acrylate with ultraviolet radiation to form a primary polymeric coating material layer surrounding the adhesion-promoting intermediary layer. The carrier gas is preferably carbon dioxide. The adhesion promoter preferably comprises a silane including, but not limited to, azidosilane, aminoalkoxysilane, polymeric silane, polymeric organosilane, organofunctional silane, vinyl ether urethane silane, organochlorosilane, silsesquioxane, polyalkoxysiloxane, and fluorinated acrylamide silane. Preferably, the adhesion promoter comprises 1,4-bis(trimethoxysilylethyl)benzene. The mixture can be atomized and vaporized. The optical fiber can also be contacted with a second liquid acrylate which is cured using ultraviolet radiation to form a secondary polymeric coating material layer surrounding the primary polymeric coating material layer. The optical fiber is contacted with the mixture of the adhesion promoter and carrier gas at a temperature below the boiling temperature of the adhesion promoter, such as about 60xc2x0 C.
The present invention relates to an optical fiber with improved adhesion characteristics. The optical fiber comprises a core, a cladding layer surrounding the core, adhesion-promoting intermediary layer comprising, a silane (preferably, 1,4-bis(trimethoxysilylethyl)benzene) surrounding the cladding layer, and a primary polymeric coating material comprising a liquid acrylate compound surrounding the adhesion-promoting intermediary layer. The fiber can also comprise a secondary polymeric coating material surrounding the primary polymeric coating material, wherein the secondary polymeric coating material comprises a liquid acrylate compound. The optical fiber can also comprise an ink coating material surrounding the secondary polymeric coating material.
The present invention also preferably relates to an optical fiber ribbon comprising a plurality of coated, substantially coplanar optical fibers, each comprising a core, a cladding layer surrounding the core, an adhesion-promoting intermediary layer comprising 1,4-bis(trimethoxysilylethyl)benzene surrounding the cladding layer, a primary polymeric coating material comprising a liquid acrylate compound surrounding the adhesion promoting intermediary layer, and a ribbon matrix material which maintains substantially coplanar alignment of the plurality of coated optical fibers. The fibers within the ribbon can also comprise a secondary polymeric coating material surrounding the primary polymeric coating material, wherein the secondary polymeric coating material comprises a liquid acrylate compound. The optical fiber can also comprise an ink coating material surrounding the secondary polymeric coating material.